Computer randomly shuts off?

[undercode100]

Hi guys so this is my first pc build , for some reason my computer wont start straight away. i have to click the power switch multiple times,i have to turn the on and off multiple times on the power supply, or take out the power lead and plug it back in. On 2 occasions it has randomly shut off. Also when i take out my mouse and plug it back in (usb), its shuts down also. I am confused, it will do everything else fine play games, stream, internet browsing, downloading, watching dvd's. It just takes a lot of messing around with stuff to get it to start up. Could it be the power supply? 

 

Any help is much much appreciated, thanks 

[Vivilacqua1]

specs?

[undercode100]

specs?

i7 4790k

 msi motherboard gaming 5

cooler master v850 psu

nvidia gtx 960

1tb wd black

240 ssd

16gb ram